[Rixson]

The existing water heater is the one with the heat exchanger in it. Thinking to put a regular hot water heater n bypass the exchanger. 

I'm curious what other people have been doing... with regards to up this age of coach and these water heaters.

If I take if I disconnect the heat exchanger hoses from the hot water heater. Am I gonna get coolant everywhere. Or is drained  back in the coolant tank? 

How much do I need to manage that

[Richard]

That coolant loop is tied into the engine. It will NOT drain on its own. If elect to replace with a conventional hot water heater, then either plug the hoses or connect them. A couple of pinch hose pliers will minimize the mess

[Jack Houpe]

Ron, West Marine has a few 120vac water heaters with heat exchanger built in them a couple positive aspects of having the heat exchanger is being able to preheating the engine in the winter along with free hot water going down the road. Richard is right about the system is open to the entire cooling system so when it starts dumping it will not quit till all the antifreeze is on the ground I put 3/4" brass ball valves on both in and out of the system for maintenance purposes.